The invention relates to an electro-optical switching device comprising a metal-compound containing switching layer. The invention also relates to applications of such a switching device.
In the relevant switching devices, the optical properties are governed by an electric potential or current.
For example, electrochromic devices are well-known, in which a layer of an electrochromic material, such as MoO.sub.3, is sandwiched between two transparent electroconductive electrode layers, for example, of indium-tin oxide. A layer of an H.sup.+ - or Li.sup.+ -ion-conducting material is present between an electrode and the electrochromic material. The device also comprises an ion-storage layer for storing said ions. The application of an electric potential of several volts across the electrodes causes the transmission or colour of the layer stack to change. Said transmission change is reversible. Electrochromic materials are used, for example, in variable-transmission windows for buildings and anti-dazzle mirrors in cars.
A drawback of oxidic electrochromic devices is that an extensive layer stack is required for their operation. A further important disadvantage is that such materials enable only a relative small transmission change, and hence a small contrast, to be attained.
In the non-prepublished international patent application IB 96/00365 (PHN 15326) filed by applicants, a switching device is described in which some trivalent metals, like Y and La, can reversibly be converted from a dihydride state into a trihydride state by supplying hydrogen. Both states have different optical and electrical properties. The dihydride state is metallic and mirror-like, whereas the trihydride state is semiconductive and transparent.